The overall objective of this project is to conduct IND-enabling drug development of a new small molecule radiomitigator based on the RP239 lead structure thru a partnership between the University of Tennessee and RxBio. Inc. This objective originates from a decade-long radiomitigator research that identified and validated the lysophosphatidic acid (LPA) G protein-coupled receptor (GPCR) subtype 2 (LPA2) as a therapeutic drug target for radiomitigation. RP239 is a specific small molecule agonist of LPA2. This proposal builds on our past experience and success developing octadecenyl thiophosphate (OTP) as a radiomitigator of the gastrointestinal acute radiation syndrome (GI-ARS). OTP licensed to RxBio Inc. was entered into the FDA regulatory pipeline under the sponsorship of BARDA in 2011. RP239 when applied +24h after LD90/8-10 (16.59 Gy) partial-body ?-irradiation with 5% bone marrow shielding reduced mortality of mice from the gastrointestinal acute radiation syndrome (ARS) by 72% (11/14 survival vs. 1/14 in placebo). RP239 and its analogs were also effective in reducing mortality due to the hematopoietic ARS. Importantly, when treatment was delayed to +48h post-total body irradiation, 50% of the mice survived in the RP239 treatment group compared to 21% in the placebo group. Its drug-like properties, combined with its specificity to the LPA2 receptor and lack of toxicity at therapeutic doses lead us to hypothesize that RP239 should be further evaluated as a potent radiomitigator of the mixed ARS elicited by high-levels of radiation. Our unique resources and experience with the development of OTP provide us with qualifications to take the RP239 lead on a development path that will qualify this new radiomitigator for fast tracking by the FDA under the animal rule.